Is my motor dead/dying?
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  1. #1
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    Default Is my motor dead/dying?

    Without too much fluff, here's the situation: 1939 Warner & Swasey No.2 turret lathe. 2-speed "consequent pole" motor, 2-1/2HP, 880 RPM and 5HP 1730 RPM.

    Probably-original contactors were in workable, but sad shape. Board regular SAF volunteers to put me together a new set of starters, and being electrically incompetent, I readily agree.

    Said shiny new starters arrived today, pre-wired and pretty much plug-and-play. I followed the instructions that he and I had been going over, in an attempt to get this antique wiring correct, and with some trepidation, fired it up.



    And it worked great!

    Both high and low speed, tried several gearbox speeds, clutches engage nice and smooth, brake works just fine, reverse works (geared, not electrical) and so on. Everything's cherry.



    I stop the motor, swap collets to throw in a different chunk of scrap aluminum so I can try some "first chips" with a still-new-to-me, and newly-refurbished machine.

    And now it doesn't want to start.

    I push the low speed button and it tries to get rolling, but is audibly struggling. After three to five seconds, the breaker for the rotary trips out. (30 amp breaker on a 50 amp circuit.)

    I changed nothing electrically. I didn't even shut the rotary off. The headstock is out of gear, and I can roll the motor pulley and belts by hand, easily.

    I'm assuming, for the moment, that the contactors are good, the wiring is good, the buttons are good, etc. because it was all working fine just minutes prior. And I got no smoke, no electrical smell, none of the wires felt hot, etc.

    That, unfortunately, leaves the motor. It's an antique, some eighty years old, and has been run on a static converter for more than a few years. (Albeit with only very occasional use in that time.)

    Did that brief use on full, proper 3-phase, maybe two minutes of operation, finally break the proverbial camel's back? Varnish going bad, maybe? An internal wire losing it's insulation?

    I plan on trying it again in the morning, to see if it's still bad, or if I get another single use out of it- which would indicate something's overheating?

    Open to other options or suggestions. Things to try? Things to look for?

    Really hoping I don't have to have this monster rewound. I have a very reputable shop less than 10 miles from here, but I can easily see it costing a grand or more.

    Doc.

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    What you describe sounds like dropping a phase, I would troubleshoot the wiring from source to motor

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    Default Troubleshooting, 2Spd motor and controls.

    Doc, it sounds like you are only getting 1Φ power to the motor, it overdraws 1Φ current and hums until the breaker trips.

    Could be a few different things, not necessarily the motor. If it lasted this long I doubt a 2 minute run caused it to give up.

    Most likely it is a bad connection somewhere. Could be in the RPC, the starter connections, the starters themselves, or the connections to the motor.

    Your RPC is new also, if I recall correctly? So don't rule that out just cause its new.

    Best way to approach it is to completely disconnect your 2Spd motor wiring from the starters, no need to stress it any more than necessary.

    Fire up the RPC and test for proper 3Φ at the line terminals of the starter. If that is correct, then engage the starter in HI speed.

    Test for proper 3Φ at the bottom of the HI speed starter. T6, T4, T5 If that is correct, connect a spare 3Φ motor to T6, T4, T5.

    Engage the starter in high speed, if the spare motor starts and runs, that indicates the the problem is downstream from the starters.

    At any point your testing fails, look further upstream for the problem. Check all of the connections, including factory ones in the RPC and the motor starters. That should lead you to where the problem exists.

    If all of that test fine, only then, would I suspect the motor. But then you may need to check those motor lead extension splices you were trying to avoid.

    I'm sure you'll let us know. SAF Ω

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    Doc, it sounds like you are only getting 1Φ power to the motor, it overdraws 1Φ current and hums until the breaker trips.
    -It does actually try to turn, but slowly. Maybe 100-150 RPM?

    I'm going to try and get my 'Sparky' over to help me diagnose, a little later today. I know the work isn't difficult, but I want to make sure I'm doing it right.

    And I still need to know how much I owe you.

    Doc.

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    Make sure that the control is not trying to run both speeds at the same time, the smoke will come out! Too late now it might have been a better fix to hook the motor on high and use a vfd...Phil

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    Quote Originally Posted by Phil in Montana View Post
    Make sure that the control is not trying to run both speeds at the same time, the smoke will come out!
    -It'd already run for some two minutes, previously, and ran perfectly. I made no electrical changes between it running perfectly and it not wanting to run at all.

    Too late now it might have been a better fix to hook the motor on high and use a vfd.
    -I'd originally considered that, but it is, after all, a turret lathe. I fully intend to do things like tapping and die-head threading, and as such, I have to have the full range of speeds.

    A VFD would have significantly reduced the utility of the machine.

    Doc.

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    The simplest test for the motor is disconnect it from all switchgear, and check the resistance of each winding, will be six, correct? Make a table and fill in the resistance of each wire to the other five.

    Then check from any one winding to ground,

    The first numbers will be around an ohm, see if you can find a DVM that gives you at least one digit after the decimal. You probably should use the 'realtive' function if it has one, to zero out the lead resistance.
    You will find there are three distinct values.

    The isolation should be over 20 megohms, which is probably what your DVM maxes out at.

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    Variation on that.....

    Disconnect from the RPC, AT the RPC.

    Check resistance from there.....Wedge the contactor closed (I assume you know it is closing) and measure the motor windings from there.

    If all OK, check RPC output.

    If NOT OK, then you need to trace the bad circuits and find out where and which one of them is open.


    If all OK there also, take out your wedge and repeat your power test, and see if anything changed. Pay attention to contactors and verify all close.

    If not OK, then the resistance check may be bogus, see if the wires all have voltage on the motor end.
    (Motor may be disconnected for that test.)

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    Solved! (Well, kind of... I think.}

    Turns out the issue was... actually kind of a nonissue. I poked around at it this morning, starting with the simple expedient of plugging my surface grinder into the rotary. That worked perfectly, with both the spindle and vacuum running smoothly and quietly- certainly not the hum or noise one would expect if it were down a leg.

    I then tried putting a spare motor on the high-speed contacts, as suggested. That, too, spun up instantly and ran quietly.

    So I tried hooking the lathe motor back up, but got the same thing. When starting it in low, it turned slowly, but struggled. I stopped it after a few seconds before the breaker could pop.

    Not really knowing what else to do, I tried the "High" button- and it came right up to speed, easily and properly.

    But in low.

    I then hit the "low" button, and it wound up to high speed, again, smoothly and properly.

    Which actually tracks with the consensus I've heard from a couple other W&S owners; the machines generally don't like trying to start in high range, and will often struggle to do so. The trick, therefore, is to start it in low, and once it's up to speed, then switch to high.

    So it works, but the buttons are reversed. Which kind of doesn't make sense, because I'm reasonably sure the first time I tried it, I did in fact push the 'low' button and got low speed. It was only the second time operating it- from a standing start- that 'low' tried to give me 'high', and struggled to do so.

    My only explanation there is that I wasn't paying quite as close attention as I thought, and did, in fact, initially push the 'high' button.

    Keeping in mind I've been handling the loose button panel gingerly and with rubber gloves, considering all the open contacts carrying 240V on the back.

    I wasn't at all sure if I should swap the motor leads at the starters, or just swap the button leads, so I opted to tweak the buttons. Here's the current button wiring:



    In this arrangement, it appears to work perfectly. The only thing I don't know is if I'm using the "wrong" starter on the 'wrong' pole. I can, of course, swap the motor leads, and return the button wiring to the previous configuration, if necessary.

    In any case, at the moment it works perfectly. It comes up to speed in low, with no struggle, and then ramps up to high almost as easily.

    I didn't really have any proper tools mounted, save for the rear-carriage parting tool, so I gave that a try. And, of course, no sweat. A nice smooth cut, no issues, no grabbing.



    No, not exactly a huge challenge, but still satisfying considering I've owned this beast for almost four months now, and have only seen it actually turn under it's own power, like, twice.

    Anyway, again, big thanks to SAF for putting the starters together, and sussing out all the wiring for me. I literally couldn't have done it on my own.

    Doc.

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    Lightbulb

    Doc, glad to hear you got it fingered out, Alaska is a long way to go for a service call.

    Wondering how well the packaging survived the trip?

    Couple of pointers when wiring it up permanently. Never interchange the motor leads at the bottom of the starter. As noted on the GE starter drawing I made, if not followed exactly as shown, the motor could be slammed into reverse at a speed change, it wont like it.

    Further, the starter shorts together half of the winding's in the low speed mode, it wouldn't like that in the high speed mode.

    I neglected to send you some tags for the motor leads, but they should be relabeled for future reference, to the standard NEMA numbers. It took considerable effort and time to deduce the proper motor lead wiring labels (A-F) from your photos, in order to make the print for your old GE starter and convert them to NEMA nubers (T1-T6) in order for it to work properly the first time.

    As noted on your GE drawing, if the rotation needs to be reversed, ALWAYS DO IT ON THE LINE SIDE, of the starter. The generated leg of the RPC (high leg) should be landed on the L3 terminal of your starter. L1 & L2 supply the control power.

    I would also suggest that you try and get some lube into those motor bearings, it's probably been a long time, and that is another issue that could send you off to the motor shop in the future. check for oil cups or grease fittings.

    As to your button wiring, I only ever seen the rear side of the contacts, I recall you mentioning that on the GE drawing I made, they were labeled in reverse. Your startup issues, sounds like a similar problem. But now that it is fingered out, make a small drawing and glue it inside the enclosure lid, for future reference if you have problems with the buttons or contacts in the future.

    If you look at the AB OEM drawing there are 2 ways to wire the buttons for different starting modes. But I doubt that you would need to change now, being that you are the operator and now know to start in low speed.

    What did you decide on mounting for the controls, wall or machine mount? That's why I gave you extra control wire length, even though you told me not to provide it. Hope there is enough for your planned location.

    i will send a mail with costs in the next couple days, SAF Ω

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    Quote Originally Posted by SAF View Post
    Doc, glad to hear you got it fingered out, Alaska is a long way to go for a service call.
    -Yeah, but if you waited 'til summer, you could get some fishing in.

    Wondering how well the packaging survived the trip?
    -Quite well. There was no real handling wear on the outside packing, and zero damage to the inner packing.

    Never interchange the motor leads at the bottom of the starter.
    -I recalled you had said something like that, which is why I opted to change it at the buttons first. I'd have asked before swapping motor leads.

    I neglected to send you some tags for the motor leads, but they should be relabeled for future reference, to the standard NEMA numbers.
    -No worries, I have a booklet of tags, my neighbor has given me a couple over the years. I plan to label everything thoroughly when I do the final installation.

    The generated leg of the RPC (high leg) should be landed on the L3 terminal of your starter. L1 & L2 supply the control power.
    -I will check that, thanks. I have no idea where it is at the moment.

    I would also suggest that you try and get some lube into those motor bearings[...]
    -I looked into that, but I saw no obvious zerks, cups or plugs. There's some grunge, so I plan to take a closer look, but my Service Manual also doesn't mention anything about lubing the motor, so I assumed they were sealed.

    But now that it is fingered out, make a small drawing and glue it inside the enclosure lid, for future reference if you have problems with the buttons or contacts in the future.
    -Already working on that very thing. I plan to print out a color copy and put it inside the enclosure, and another that I'll print on the same kind of light card stock the Service Manual pages are printed on, and put it in there, too.

    The Manual is basically a 3-ring binder, so I plan to add several pages, detailing what I know of the machine's history, the changes I made (like the oil pump belt idler) and so on. I might even tape a CD with all the photos I took, in there.

    If you look at the AB OEM drawing there are 2 ways to wire the buttons for different starting modes.
    -The only difference between them was one won't let the operator switch from high to low without stopping first. I assumed that was to reduce back EMF which might screw with other machines in a plant. Just a guess, though.

    What did you decide on mounting for the controls, wall or machine mount?
    -The current plan is to make a mount to attach it to the machine in the back left corner, by the belt cover. I think I'd prefer the machine be self-contained, and not have parts bolted to the wall.

    I'll eventually run a conduit over from the rotary, but for now, I have what's basically a 30-foot cable to plug it in directly.

    I will send a mail with costs in the next couple days.
    -Much appreciated, again. You were a big help on this project.

    Doc.

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    I have had the VFD on a two speed motor come up several times recently. The latest is a cold saw so old that no one at the factory remembers it and they have no information on it. It turns out that apparently the original designer thought he needed both speeds along with a VFD. What I wound up doing was duplicating the changes the factory has made over the years. They had found that a two speed motor on a VFD has almost no improvement in use, especially if the spindle has gears to reduce the speed. A two speed motor running at full speed and full load draws rated current. The motor running at half speed and rated load draws the same current at half the speed and delivers half the horsepower of full speed, same torque and half RPM. A two speed motor running in the full speed connection with a VFD reducing it to half speed delivers half horsepower at the same current. Having the motor in the half speed connection may give some improvement at very low speeds, but not worth the trouble. At any normal speed it is hard to tell the difference. The saw company now uses a standard motor and a VFD.

    Bill

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    There are motors made for two speeds that have constant HP in the two speeds, they draw more in the slow speed and double their torque. Those would make a difference.

    Looking up the type, I noticed (surprise!) that one prime application of those constant HP motors is on machine tools.....
    Last edited by JST; 11-22-2020 at 02:31 AM.

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    Interesting. The cold saw motor is the typical Dahlander that has the same torque at both speeds. As you certainly know, more than I do, such a motor does not simulate a gearbox. I got my Sheldon lathe without a drive because the factory was going to put in an experimental variable drive but got out of the manual lathe business before they got to it. The standard setup was a 5 hp motor with a four speed gearbox plus back gear, giving eight speeds with proportional torque. I installed a 15 hp DC motor with belting to give 2,500 RPM max, which is a bit scary on a 15" swing lathe and I have never used it that fast. Of course, at 500 RPM I am only getting 3 hp, but that is about the maximum load for the lathe. It's a great lathe but it ain't no American Pacemaker or Monarch 61, an accurate medium duty lathe.

    Can you give us a link to the motor you describe? I can think of ways to do it, but I have never seen one.

    Bill

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    Wild guess but constant hp, multispeed motors are probably not dahlander - wound, but have two independent windings.

  20. #16
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    Default 3Φ, Single Voltage, One Winding, Two Speed Motor Types

    3Φ Single Voltage, One Winding. Two Speed Motor Types
    constant-hp.jpg
    constant-torque.jpg
    variable-torque.jpg
    SAF Ω
    Last edited by SAF; 11-22-2020 at 06:57 PM. Reason: Addition

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    Those are constant torque types, not constant hp.

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    There is no way around it, torque is related to flux density.

    Typical 2 speed motors are connected in series like a 480v 9 wire motor, but for the low speed they are connected in anti series which preserves 240v across each coil, forcing the magnetic fluz to find a return path between the coils. 2 speed motors have to be short pitched and lower flux density so that there is a magnetic pathway for the flux to go, otherwise they would burn out.

    For what its worth, you can take a 4 pole shaded pole fan motor, connect 2 coils in series, the other 2 coils in series with a run capacitor and operate it from a 60vac supply and turn a 1700 rpm fan motor into 3400.


    Anyhow, rather than connect your two speed motor in anti series for low speed (like a 9 wire motor wired wrong)


    You can instead bring out all 12 wires and wire it in anti series delta for low speed and series y for highspeed.

    You will then get about the same power at both speeds.

    But you still need a motor sized for the torque you need produced via consequent poles at low speed. As such they are large and heavy.

    The 4 speed motors on a certain type of submersible ship have 4 separate coils. Redundancy and its a pump load so 100hp at 1800 rpm is more like 2 hp at 600rpm


    Another connection would be anti parallel y for low speed and series delta for highspeed or series y for high speed.

    All you are doing is just changing thr coil connections to get thr flux densith3 what you want it to be.

    There motor still has to be large enough to supply the torque you want at the lowest speed, with most motors under 100hp the iron losses are small, there isnt any benefit other than small gains in efficiency for producing anything othrr than a constant torque 2 speed motor.

    An intermittant duty cycle high torque slow speed vs low torque high speed could be convienient for some things, not sure what...

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    Might be real interesting to take a standard 4 pole 3 phase motor and bring 24 wires out.

    A standard 9 wire connection for 240/480v. 4 pole 1800rpm.

    And a 24 wire connection for 240v only, connecting 2 poles in y for high speed and thr other set of poles gets connected in y but with 3 run capacitors wired in series.

    You just might get a higher torque density at low speed than would be possible with a consequent pole winding, while preserving theoretically the same torque at highspeed, provided the run caps are optimally sized and dont oversaturatte the motor at low loads.


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